This application claims priority of Japanese Patent Application No. 2000-009409 filed on Jan. 18, 2000 and of Japanese Patent Application No. 2000-012256 filed on Jan. 20, 2000. The complete disclosures of both applications are hereby incorporated by reference.
The present invention relates to an automatic balancing apparatus which reduces vibrations of a rotational shaft during the rotation of a rotor such as a motor.
Many electric appliances, such as computers, are such that a rotor is rotated by a motor and the like. For example, a recording and regenerating apparatus placed in a computer and a CD player has a mechanism to rotate a disc as a recording medium. In recent years, such apparatus are required to accommodate super high speed rotations of 6,000 to 10,000 rpm. Therefore, vibrations of the rotor occur especially when it rotates at a high speed as the rotation exceeds the resonant frequency. The rotational vibration (end play) results in a variety of problems, such as tracking errors.
As a solution to the above issue, for example, a rotation control apparatus is suggested in Tokkai H10-257710. FIG. 1 is a longitudinal section of a spindle motor to which the rotation control apparatus of Tokkai H10-257710 is attached. FIG. 2 is a cross section of a main part of the rotation control apparatus.
As shown in FIG. 1, spindle motor 51 is comprised of: stator 53 which is fixed to hub 52; rotor 54 which has permanent magnet 54a placed across from stator 53; and spindle shaft 55 which is fixed to the center of rotation of rotor 54. When stator 53 is magnetized as electricity flows therein, the magnetic field, which rotates rotor 54, is generated between stator 53 and rotor 54. As a result, rotor 54 rotates together with spindle shaft 55.
Rotation control apparatus 56, as shown in FIGS. 1 and 2, is comprised of case 57, which is mounted to spindle shaft 55 such that spindle shaft 55 passes through the inside, and a turntable (not shown in the figures). Case 57 and the turntable rotate together with spindle shaft 55.
A ring-shaped space is formed around the shaft inside case 57, and magnet 58 is placed at the innermost portion of the space. Magnet 58 is bipolarly magnetized in the vertical direction (the axial direction of spindle shaft 55). Additionally, a plurality of balancer balls 59, made of a magnetic body, are placed on the outer circumference of magnet 58 in the space of case 57. Balancer balls 59 are drawn up and fixed to the outer circumference of magnet 58 by the magnetic force.
With rotation control apparatus 56 as configured above, balancer balls 59 rotate together with spindle shaft 55 (or rotor 54) while being fixed on the outer circumference of magnet 58 when spindle motor 51 is started. Once the rotational speed of spindle shaft 55 (or rotor 54) gradually increases and exceeds the resonant frequency, balancer balls 59 are separated from magnet 58 and move towards the outer wall 57a of case 57. As a result, the rotational vibrations of spindle shaft 55 (or rotor 54) are reduced by the effect of balancer balls 59.
As described above, the rotation control apparatus 56 of Tokkai H10-257710 reduces the rotational vibrations of spindle shaft 55 (or rotor 54) when the rotational speed of spindle shaft 55 of spindle motor 51 increases and exceeds the resonant frequency. As a result, tracking errors and the like can be prevented.
However, such an apparatus has a configuration in which the outer circumference of magnet 58 is bipolarly magnetized in the axial direction such that balancer balls 59 are fixed to the outer circumference of magnet 58 when the rotation is less than the resonant frequency. Therefore, balancer balls 59 are not placed on the outer circumference of magnet 58 with equal distance from each other, for example bunching up together, when spindle motor 51 is suspended. As a result, the rotational center is deviated when the motor is resumed, causing a loss of balance in the rotation. Consequently, the rotational characteristics of the apparatus are lowered when the motor is in motion.
Moreover, balancer balls 59 are fixed on the spherical outer circumference of disc-shaped magnet 58 only by the magnetic force. This means that the force of magnet 58 to hold balancer balls 59 is weak in the tangential direction. Hence, fixation the fixing force (holding force) to balancer balls 59 is weak at the beginning of the rotation, and balancer balls 59 tend to shift in the circumferential direction with the centrifugal force at the beginning of the rotation. In addition to the deviation of the rotational center, bumping sounds are caused when balancer balls 59 collide with each other. Further, the shift of balancer balls 59 at the beginning of the rotation tends to amplify the vibration at the rotational center, causing a decrease in the rotational characteristics when the apparatus is started.
Rotation control apparatus 56 as described above reduces the rotational vibrations when the rotation of rotor 54 exceeds the resonant frequency. However, when the speed of rotor 54 continually increases and exceeds a given value, the apparatus can no longer control the vibration. In other words, a range of rotation in which balancer balls 59 shift in the circumferential direction but on the same radius line to reduce the rotational vibrations is limited to a given band of rotational frequencies. Therefore, once the rotation reaches the given speed, the effect of reducing the rotational vibrations cannot be performed.
One may reduce the rotational vibrations in a rotational range with higher speed by establishing the resonant frequency of rotor 54 higher than as described above. However, with such establishment, balancer balls 59 do not function to reduce the rotational vibrations until the speed reaches the resonant frequency, rather they increase the vibrations. Therefore, the rotational vibrations become at low rotation speed, less than the resonant frequency become an issue.
Hence, the present invention intends to provide an automatic balancing apparatus which prevents a decrease in the rotational characteristics when a motor is started by firmly fixing balancer balls on the outer circumference of a magnet with equal distance from each other when the motor is at rest.
Additionally, the present invention intends to provide an automatic balancing apparatus which reduce rotational vibrations corresponding to any rotational speed, such as in the case of the low speed rotation, when the rotation of the rotational body is less than the resonant frequency, and in the case of the super-high speed rotation, when the rotation exceeds a given value above the resonant frequency, as well as in any other cases.
In accordance with one aspect of the invention, an automatic balancing apparatus is disclosed which comprises: a support shaft which is rotated by a drive; a case body which is fixed to the support shaft and which rotates together with the support shaft; a ring magnet which is placed at the inside corner, in the radial direction, of an inner space of the case body; and a balancing member, the balancing member further comprising a plurality of magnetic bodies which are movable in the inner space of the case body and which can be drawn up by the magnetic field of the ring magnet; wherein, when the rotational frequency of a rotor, which rotates together with the case body, exceeds the resonant frequency, the automatic balancing apparatus reduces vibrations of the rotor; and the outer circumference of the ring magnet has a flat portion.
In accordance with another aspect of the invention, an automatic balancing apparatus is disclosed which comprises: a support shaft which is rotated by a drive; a case body which is fixed to the support shaft and which rotates together with the support shaft; a ring magnet which is placed at the inside corner, in the radial direction, of an inner space of the case body; and a balancing member, where the balancing member further comprises a plurality of magnetic bodies which are movable in the inner space of the case body and which can be drawn up by the magnetic field of the ring magnet; wherein, when the rotational frequency of a rotor, which rotates together with the case body, exceeds the resonant frequency, the automatic balancing apparatus reduces vibrations of the rotor; and the outer circumference of the ring magnet has a number of magnetized portions wherein the number of the magnetized portions is equal to or higher than the number of the balancing member.
In accordance with yet another aspect of the invention, an automatic balancing apparatus is disclosed which comprises: a support shaft which is rotated by a drive; a case body which is fixed to the support shaft and which rotates together with the support shaft; and a plurality of balancer members which are movable in a inner space of the case body; wherein, when the rotational frequency of a rotor, which rotates together with the case body, exceeds the resonant frequency, the automatic balancing apparatus (1) reduces vibrations of the rotor; and (2) the inside of the case body has (i) a holding portion which prevents the plurality of balancer portions from moving outward in the radial direction when the rotor is at rest and at the beginning of the rotation of the rotor; (ii) a first operating portion which reduces vibrations of the rotor by preventing the plurality of balancer members from further shifting outward in the radial direction when the shift of the balancer members occurs with the holding force of the holding portion as the rotational frequency of the rotor exceeds the resonant frequency; and (iii) a second operating portion which reduces vibrations of the rotor, rotating at a rotational frequency exceeding a given value, by preventing the balancer members from further shifting outward in the radial direction beyond the first operating portion when the rotational frequency of the rotor exceeds the given value which is beyond the resonant frequency.
In accordance with still another aspect of the invention, an automatic balancing apparatus is disclosed which comprises: support shaft which is rotated by a drive; a case body which is fixed to the support shaft and which rotates together with the support shaft; a ring magnet which is placed at the inside corner, in the radial direction, of an inner space of the case body; and a balancing member, where the balancing member further comprises a plurality of magnetic bodies which are movable in the inner space of the case body and which are drawn up by the magnetic field of the ring magnet; wherein, when the rotational frequency of a rotor, which rotates together with the case body, exceeds the resonant frequency, the automatic balancing apparatus reduces vibrations of the rotor; and the outer circumference of the ring magnet has a flat portion.
In accordance with even still another aspect of the invention, an automatic balancing apparatus is disclosed which comprises: a support shaft which is rotated by a drive; a case body which is fixed to the support shaft and which rotates together with the support shaft; a ring magnet which is placed at the inside corner, in the radial direction, of an inner space of the case body; and a balancing member, where the balancing member further comprises a plurality of magnetic bodies which are movable in the inner space of the case body and which are drawn up by the magnetic field of the ring magnet; wherein, when the rotational frequency of a rotor, which rotates together with the case body, exceeds the resonant frequency, the automatic balancing apparatus reduces vibrations of the rotor; and the outer circumference of the ring magnet has a plurality of magnetized portions wherein the number of the magnetized portions is equal to or higher than the number of the balancing members.